JPS6150648B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for diffusing added ammonia as a reducing agent into the exhaust gas to be treated in a catalytic dry denitrification apparatus.

When removing nitrogen oxides from exhaust gas,
Dry denitrification methods that use an ammonia reducing agent and bring it into contact with various denitrification catalysts are widely used. By the way, the effective denitrification reaction of ammonia, which is a reducing agent, must be uniformly mixed during exhaust gas transport, and in this case, the added ammonia is usually not mixed sufficiently into the exhaust gas flow. Therefore, some ammonia was supposed to be discharged from the reaction system without being able to participate in the reaction. Such excessive ammonia may cause new secondary pollution. Furthermore, if sufficient mixing is not possible, there is a drawback that more ammonia than a predetermined amount is required to achieve a predetermined denitrification rate.

The present invention diffuses the added ammonia into the exhaust gas so that it can be sufficiently mixed with the exhaust gas to be treated.
This problem was solved by installing multiple stages of grids in which disturbance members such as square timbers were arranged in front of the ammonia inlet, and by adding a porous dispersion plate to the inlet cone of the denitrification device behind it. .

For example, in the conventional method, in addition to arranging a plurality of injection ports, in order to further improve dispersion, the injection port is also used as an injection nozzle. However, because the nozzle is made small or narrow in order to be used as an injection nozzle, adhesive substances or ammonia compounds in the exhaust gas to be treated stubbornly stick to the area around the nozzle, which not only worsens the spray condition but also leads to nozzle blockage. This has the disadvantage that frequent cleaning of the nozzle portion is required. However, in the present invention, the injection diameter is pipe-shaped, which avoids the problem of large diameter, and also eliminates the need to expect a diffusion effect from the nozzle. A porous dispersion plate provided in the section allows effective diffusion of a small amount of added ammonia.

In this way, the present invention was proposed in order to solve the problems seen in the prior art when diffusing an ammonia reducing agent into exhaust gas in dry denitrification, but especially at low load. Good diffusion is also achieved, and even if the amount of exhaust gas is large or the equipment is large, uniform mixing of ammonia and exhaust gas is possible.

In particular, the diffusion of added ammonia according to the present invention not only solves the problems seen in the conventional technology, but also
In its configuration, a porous dispersion plate installed at the inlet cone of the denitrification equipment not only uniformly mixes ammonia into the exhaust gas, but also suppresses the uneven flow of the treated gas within the column, and the porous dispersion plate suppresses the dispersion of ammonia. Compared to the case without plates, the velocity distribution inside the column is smoothed, and the same linear velocity, space velocity, and reaction temperature are maintained for the entire catalyst bed packed in the device, which is more effective in increasing the denitrification rate. It plays a role.

The ammonia diffusion method of the present invention will be described in more detail below with reference to the accompanying drawings, but the present invention is not limited to the examples.

In Figures 1 and 2, ammonia injection pipe 1
is introduced into the exhaust gas flow path, and has a plurality of ammonia inlet ports 2 arranged at equal intervals in the length and width of this flow path cross section. Ammonia is blown in the same direction as the flow direction of the exhaust gas from this blowing port 2, and in front of the blowing port 2, there is a grid with square bars 3 arranged horizontally at the same intervals as the blowing port 2. Next, a set lattice 30 in which square timbers 3 are arranged at the same intervals as the inlet 2 is arranged in the vertical direction as well, and the inlet 2 faces the intersection of the front and rear set lattices 30, 30.
The inlet of the denitrification device 4 is formed in a cone portion 5 in which the exhaust gas flow path gradually widens, and this cone portion 5 is provided with a porous dispersion plate 6. 7 is a catalyst layer within the denitrification device 4.

Therefore, ammonia as an additive enters the duct of the exhaust gas flow path from the ammonia injection pipe 1 in a vaporized state, and is diffused and mixed into the exhaust gas to be treated through the blowing port 2. Here, the blowing port 2 at the point of contact with the exhaust gas is a simple hollow cylindrical pipe that can avoid clogging even if the duct in the exhaust gas adheres around the nozzle, and the problem was solved by blowing a jet stream. It is. The cylindrical nozzle of the blowing port 2 has an inner diameter of 5 mmφ to 50 mmφ, which is larger than conventional nozzles, and can be easily injected into the exhaust gas. To solve the problem that it is difficult to smoothly diffuse into the exhaust gas only under such conditions, we have installed multiple stages of assembled grids 30 in which square bars 3 are arranged to disturb the jet flow and promote turbulent diffusion. By providing a porous dispersion plate 6 in the inlet cone portion 5 of the denitrification device 4 at the front, a situation is created in which turbulent diffusion of ammonia into the gas is effectively performed, leading to the formation of a homogeneous mixing state. be. The assembled grids 30 arranged here are installed in front of the inlet 2 of the ammonia injection pipe 1, with the intersection of the front and rear assembled grids 30, 30 and the peak of the V-shaped square beam 3 facing the inlet 2, The ammonia fluid mass is macroscopically distributed and dispersed in all directions in the exhaust gas which is the main stream, and as an accompanying effect, the vortex diffusion by the assembled grid 30 works even more effectively to diffuse the added ammonia. Note that the square material 3 may have a semicircular cross section, a V-shape, or any other material that generates turbulent flow.

In the present invention, the porous dispersion plate 6 in front of the grid grid 30 provides a better mixing effect in homogenizing ammonia and exhaust gas. That is, when ammonia gas, which is an inflow fluid, enters the main stream of exhaust gas through the mesh grid 30, it is dispersed into small fluid masses by the action of the mesh grid 30, but the mixing is not yet sufficiently homogenized down to the molecular scale. It is thought that there are many cases where this is not the case. Therefore, the present invention uses an ammonia diffusion method that effectively grasps the fluid mixing phenomenon in which the grid grid 30 first plays a role of macroscopic mixing, and then the porous dispersion plate 6 plays the role of microscopic mixing. Therefore, the exchange rate between the mainstream exhaust gas and the added ammonia is promoted by this synergistic effect.

However, the structure of the braided lattice 30 is
When adding ammonia from the dotted line, it is preferable to arrange a disturbance material such as square timbers 3 that provide a turbulent structure in a turbulent flow field in order to diffuse in all directions and achieve macroscopic fluid mixing, and more preferably a grid grid. It is made into a shape. The porous dispersion plate 6 provided in the denitrification inlet cone portion 5 may be any type as long as it is a buff-full plate that promotes mixing in a direction perpendicular to the flow in a turbulent state, but it is difficult to manufacture and cost-effectively. A punching plate is most preferable as an inexpensive interior material that exhibits sufficient effects.

Here, the porous dispersion plate 6 as an internal device creates a vortex according to the degree of the pore diameter and promotes mixing in the direction perpendicular to the flow, thereby eliminating the non-uniformity of the added ammonia emitted from the point source. However, the treatment gas is made uniform throughout the entire region before reaching the catalyst layer. Furthermore, the streamlines of the wake containing vortices generated after the porous dispersion plate 6 tend to intersect, making the mixing characteristics even more excellent.

By providing the porous dispersion plate 6 at the inlet cone portion 5 of the denitrification device 4, not only the ammonia diffusion effect into the exhaust gas but also the gas flow passing through the catalyst packed bed 7 in the denitrification device 4 can be achieved. This also aims to avoid the channeling phenomenon in which there are parts where fluid blows through. This becomes more of a problem as the equipment becomes larger, and channeling is a phenomenon that has an adverse effect on physical and chemical operations, and particularly in dry-type denitrification equipment, it causes a significant drop in the denitrification rate. Therefore, its industrial value is extremely high. In addition, to prevent mixing of ammonia and exhaust gas and channeling of the gas flow in the catalyst-packed layer 7, the porous dispersion plate 6 can provide frictional resistance by providing it in the inlet cone portion 5, when installed in a piping duct. The flow velocity is extremely reduced compared to the above, and considering the frictional resistance that increases exponentially with the flow velocity, the present invention not only provides the diffusion effect of added ammonia with a small frictional resistance, but also provides a It also has the effect of preventing gas drift.

By the way, in the present invention, the problem of clogging of the nozzle at the ammonia spouting point due to dust such as vizine and ammonia compounds is solved by significantly increasing the diameter of the spouting port. By periodically cleaning the inlet 2 from the line or compressed air line 8, such problems can be avoided more completely. This removes scale that has accumulated not only in the ammonia inlet 2 but also in the piping path over a long period of time, and makes the amount of ammonia flowing out constant at the multiple inlets 2, which correspond to point sources of added ammonia. , it becomes possible to maintain the overall flow balance over a long period of time.

As described above, the present invention creates an excellent diffusion method that promotes mixing of a trace amount of added ammonia and the mainstream exhaust gas in a denitrification device, and eliminates stagnation that does not contribute to mixing at all in its configuration.
With a short mixing distance and low frictional resistance, the exchange rate between ammonia and mainstream gas is increased, and dry denitrification using ammonia suppresses ammonia emissions.
This method provides an ammonia diffusion method that maintains a predetermined denitrification rate, and is highly effective.

[Brief explanation of the drawing]

FIG. 1 is a front view of a device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1...Ammonia injection pipe, 2...Blowing port,
3... Square timber, 4... Denitrification device, 5... Cone part,
6... Porous distribution plate, 7... Catalyst layer.

Claims (1)

[Claims] 1. In an apparatus that uses an ammonia reducing agent to treat nitrogen oxides in exhaust gas by bringing them into contact with a catalyst,
When blowing ammonia into the exhaust gas to mix it uniformly, ammonia is blown in the same direction as the flow direction of the exhaust gas from the many blowing holes in the flue gas flow path, and then laterally in front of the blowing holes. It is applied to the intersection of a lattice-shaped disturbance member made up of a plurality of arranged rods and a plurality of rods arranged vertically with a slight interval between them, and then applied to the inlet cone of the denitrification device. A method for diffusing added ammonia in a dry denitrification equipment, which is characterized by uniformly diffusing added ammonia by applying it to a porous dispersion plate.